-LRB- CNN -RRB- -- Police in Norwalk , Ohio , are searching for a 17-year-old girl who has been missing since June 7 after trading text messages with her boyfriend that indicated the two were planning to run away together , police Sgt. Jim Fulton said Monday .

Fulton said police believe Abbi Obermiller left her grandparents ' home on her own accord late on the night of June 6 , but said detectives are `` concerned '' that the situation may have changed and that there is a `` possibility she is in danger . ''

He declined to elaborate on what information authorities have received that led them to believe her situation possibly changed .

Investigators in the case have uncovered a series of text messages between Obermiller and her boyfriend , identified by police and by Obermiller 's parents as 20-year-old Robert Young of Norwalk , that appear to be coordinating when she would be picked up from her grandparents ' home in the early morning hours of June 7 , Fulton said .

According to Fulton , Obermiller repeatedly sent messages to Young asking , `` How much longer ? ''

At 12:45 a.m. June 7 , Young responded and told her to `` leave now , '' Fulton said .

The last text message from Obermiller appeared to direct Young to her location , Fulton said .

CNN could not immediately reach Young for comment Monday night .

Young has denied knowledge of Obermiller 's whereabouts , according to police .

Young has told police the messages were a week old and were sent over Memorial Day weekend while the couple coordinated a swimming date , Fulton said .

However , other evidence indicates the couple were making plans to run away after Obermiller 's parents expressed disapproval of their relationship , Fulton said .

Young was charged June 14 with obstruction of justice in the case for his failure to cooperate in the investigation , authorities said .

A text message to one of Obermiller 's friends sent before her disappearance indicates Obermiller knew she would be going away .

In it , she tells her `` bestest friend '' that she wo n't be able to talk for a while so `` do n't forget me , '' according to Fulton .

And a note found in her grandparents ' home reads : `` I just could n't take any more of this drama , it 's not good for me . Love you all . Hope to see you soon . Love , Abbi , '' according to Fulton .

Fulton also said one of Obermiller 's friends told police she saw Abbi wearing a wedding ring .

`` We do believe that Bobby does know where she 's at , he just does n't want to tell us , '' Obermiller 's mother , Rose Obermiller , told HLN 's `` Prime News '' on Monday night .

Rose Obermiller told `` Prime News '' that she initially approved of her daughter 's relationship with Young , but that Young 's behavior grew increasingly alarming .

`` In the beginning he was a nice Christian boy , '' Obermiller said . `` He went to church , he was on the baseball team , he was on the basketball team -LRB- and -RRB- he really cared for Abbi .

`` But as it went on , he was telling her , ` No I do n't want you to be class treasurer ; no , I do n't want you to go to New York with your choir ; no , I do n't want you to see these friends and relatives , '' Obermiller said . `` He was telling her what not to do . ''

Fulton said Young has declined to take a polygraph test in the case .

@highlight

Abbi Obermiller last seen June 6

@highlight

Text messages indicate she was planning to run away with her boyfriend , police say

@highlight

Boyfriend denies knowledge of her whereabouts

@highlight

He has been charged with obstruction of justice for failure to cooperate in investigation